alt Hacker NewsShow HN: Posthorn, self-hosted mail gateway
Introducing Posthorn, a self hosted email gateway. One docker container (or Go binary) between every self hosted app on your VPS and your transactional email provider. Set up Posthorn once, point your apps to it, done.
I was trying to deploy Ghost on a DigitalOcean droplet and found that DO and many different VPS services have started to block the default SMTP ports to try to combat the various types of abuse they get. To actually configure my app, I had to hack together a Postfix relay.
In another project, I had a static site which had a contact form, but my free Formspree account was occasionally hitting usage limits and I desperately wanted some of the anti-spam features they had gated behind their paid accounts so I put together a caddy module to catch HTTP POSTs and bounce them to my provider.
I kept bumping into these same email issues. Many of the services I wanted to host (Gitea, Mastodon, Umami, Comentario) ran into the same limitations. This felt like a really common issue that had no good solution.
Posthorn is what I built to solve this. It's a small Go binary (or 10 MB docker image) that sits between your self hosted apps and your transactional email provider of choice (shipping with support for Postmark, Resend, Mailgun, Amazon SES or an outbound SMTP relay). It also accepts POSTs from HTML forms to support static site needs while adding security layers such as honeypot fields, origin checks and IP rate limiting. There's also a JSON HTTP API that supports Bearer auth for backend scripts or cron jobs that just want a /send endpoint.
I now use this personally in multiple scenarios and I've spent a lot of time beating this up and testing against what I can validate. I'd love to hear how this might be useful for you, what breaks and any feedback you might have. It's open source under Apache 2.0 and I'd love contributions. I'm planning to support and grow this for the long haul.
Code: https://github.com/craigmccaskill/posthorn
Docs: https://posthorn.dev/
Longer write up: https://craigmccaskill.com/introducing-posthorn/
Previous HN discussion on the exact issue I'm trying to solve: https://news.ycombinator.com/item?id=43620318
Comments
The title is inaccurate. Its a self-hosted transactional email gateway, not self hosted email
An interesting combination of features.
Personally, I have used nullmailer in the past to provide a sendmail compatible local install that immediately forwards email to the SMTP server of my choice. Has worked flawlessly.
Obviously, that doesn't come with HTML form support, but then I am also not sure I would like the same binary to handle both a HTTP(S) endpoint and email submission :)
Nice project, nice initial subset of options.
At work I'm using Apprise (https://appriseit.com/) to deliver notifications.
Are you planning to add more services or to limit Posthorn to emails?
I really want to try this, but I'm afraid my DNS will be blacklisted if I do. Can someone guide me and others, if this is the case? E-Mail is the most complex of everything I know in sysadmin/DNS/Server stuff.
My current provider since almost two decades without any issues, except speed and storage limitations is all-inkl.com, but I really just use it for email and nothing else, therefore most likely overpriced at ~6€/month.
I would love to switch to some VPS/root or anything where I can SSH and install, compile my own services, but something where security is high and support is 24/7 available.
I am running a local mail server using cloudflared tunnels and brevo for sending
postfix/sendmail/dovecot/ingress setup
I am really happy with the setup. (So far)
> Nobody wants to self host email server.
I do. Though I am self hosting it to have my personal email, being well... personal. Not for my company so maybe I am not the target.
Interesting project though. I always felt missing API to just send emails from some script in my mail server.
Don't services like SES already operate over 443/TLS and aren't blocked?
email.riamu.io comes to mind
> Nobody wants to run a mail server in 2026.
We do, and thats why we use Postal [1].
The more SaaS applications that self-host email the better. It forces the big guys, ie Microsoft, to improve their blocklists and not lazily block entire ranges. Yes its work contacting them occasionally, but it keeps the internet open. The alternative is an internet where they control it all.
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Confusing title, "self-hosted mail" and "self-hosted email gateway" are two quite different things :-/